Volume display optical system and method

ABSTRACT

There is disclosed a method and system for controlling the optics of a coherent light source impacting a three dimensional defined volume. The system uses a scanner to time and spatially position the coherent light. The divergent light beam output of the scanner is then placed through positive and negative lenses to narrow the beam waist while also increasing the divergence angle of the beam. Provision is made to abate the divergence angle so that the light, as it impacts the defined volume, will not continue to diverge, creating a skewed image within the volume.

This application is a continuation of Ser. No. 563,370, filed Aug. 6,1990, now abandoned.

TECHNICAL FIELD OF THE INVENTION

This invention relates to volume displays and more particularly to anoptic light ray system and method for controlling the generation oflight images within a defined volume.

This application is a continuation of application Ser. No. 07/563,370,filed Aug. 6, 1990 now abandoned.

RELATED APPLICATIONS

All of the following patent applications are cross-referenced to oneanother, and all have been assigned to Texas Instruments Incorporated.These applications have been concurrently filed and are herebyincorporated in this patent application by reference.

U.S. patent application Ser. No. 07/563,180 filed Aug. 6, 1990 andentitled "A System and Method for Support and Rotation of an Object".

U.S. patent application Ser. No. 07/563,238 filed Aug. 6, 1990 andentitled "Linear Stepper Motor Design and Method of Operation".

U.S. patent application Ser. No. 07/563,372 filed Aug. 6, 1990 andentitled "Apparatus and Method for Volume Graphics Display".

U.S. patent application Ser. No. 07/563,374 filed Aug. 6, 1990 andentitled "Volume Display Development System".

BACKGROUND OF THE INVENTION

A relatively new display system has been developed which generatesimages in all three physical dimensions. The system relies on thegeneration within a confined space, typically, a closed dome, of avolume upon which coherent light impacts to create the images. Eachimage is comprised of a number of light pixels (called voxels) usuallygenerated by one or more laser beams impacting on the generated volumewithin the dome.

The defined volume can be created by spinning a helix shaped surface(disk) within the dome so that as the disk spins a volume is createddefined by the disk surface as it moves up and down in a helical curve.Thus, at any point in time a different height of the volume is at agiven physical location within the dome. A light spot can then becreated by impacting a beam of coherent light with the disk at aparticular point in time coinciding with the height desired for thatpoint of light. By timing a large number of such light beams, threedimensional objects can be created within the dome and these objectsthen can be viewed from any position since the spinning disk (whichcreates the display volume) is essentially transparent to the eye. Sucha system is the subject of U.S. patent application, Ser. No. 07/409,176.

One critical aspect of such a system is the very fast processing andgeneration of the light points which are distributed in space and timeand which must be very precisely timed and spatially positioned if theresulting image is to be free of jitter. Thus, it is necessary togenerate signals representative of the light points that are desired ona continuing basis and then to direct the laser light beams to thosepoints at precisely the right physical location and at the precisely theright time.

A further requirement of such a system is that different light colorsare required and these must all be positioned to impact at the sameprecise point.

One goal of such a system is to generate images from known x,y,z dataand then once the images are generated, to actually display them in thecreated volume. This presents several optical challenges in the designof the system. Some of these problems include the coverage of the entirevolume, the trade-off between resolution and speed, and how many pointsto display and with what resolution. Some of these trade-offs stem fromhow quickly a signal can be switched from one point to another withinthe volume versus how small the point can be focused.

The optical problem begins with the fact that the scanner has a verylimited output divergent angle and thus, it is important to amplify thatdivergence to fill up the display volume optically. However, when thatangle is diverged, the width of the laser beam is also diverged. Thedivergence reduces the resolution of the beam.

A set of signals must be generated to drive the acousto-optics at theproper time. The image that is produced is critically dependent on thattiming and on the spatial positioning of the modulated coherent lightbeam. In order to achieve a 3-dimensional image, beams may beintercepted by the helical screen at any depth in the volume. Thisrequires the beams to maintain a small diameter throughout the pathlength inside the volume display in contrast to typical laser printersor projectors where a small focus is achieved only in a single plane.

Thus, there exists in the art a need for an optic system that works atextremely high speeds and that can both spatially and temporally controlthe positioning of coherent light beams.

A further need exists in the art for such a system and method whichallows for different colors of light and which allows for each lightcolor to be positioned in exactly the same physical space.

A still further need exists in the art for such a system which allowsfor easy adjustment for different created volumes and which can handledifferent disk shapes.

SUMMARY OF THE INVENTION

The problems of presenting three dimensional images have been solved bypartitioning the system into real time and non-real time components.This invention deals with the real time elements as well as the opticswhich support the operation. The system uses a processor which thendrives the display. The processor in one embodiment is a dedicateddevice that accepts display lists of information and generates commandsthat drive a scanner. The scanner then generates the deflection of thelaser beam in real time to create the image in the created volume.

The problem of diverging the individual light beams while maintainingfocus resolution is solved by placing a positive lens close to thescanner output to converge the laser beam width so that is has a verysmall waist. Then a negative lens is used to amplify the divergencecreated by the scanner. This lens is designed to have very little effecton the laser beam diameter because the waist is small as the beam passesthrough the negative lens.

The laser beams will continue to diverge with respect to each otherafter passing through the negative power lens. Thus, when they impactthe volume at different depths, the size of the image will be differentdepending upon the volume distance from the lens at the point of impact.To prevent distortion of the resulting image, another optical element isused in order to collect the diverging light beams and make them gothrough the volume parallel to each other.

In one embodiment, a mirror is used. However, any other type ofrefracting or diffracting element that gives the same power can be used.

An additional problem that was solved is the multicolor problem which isa matter of taking separate systems, one for each color, and combiningthem so that they all strike the volume in the right locations. Threeseparate lasers are used (for 3 colors) having a separate scanner foreach color. Before the beam is diverged, the colors are mixed forpresentation to the negative lens.

Accordingly, it is one technical advantage of this invention to providean optical system that can accept signals representative of the time andspatial orientation of a plurality of coherent light spots in a definedvolume and to convert those signals into spatially separated, narrowlyfocused, coherent light beams. At their point of impact, these beamsmust be parallel to one another.

It is a still further technical advantage to construct such a systemhaving multicolor presentation, with each color having the capability ofpresentation at the same spatial position within the defined volume.

It is a still further technical advantage of this invention to provide asystem for presenting three dimensional images by the use of modulatedcoherent light where the light is separated into time and spacecoordinates and where the individual beams are narrowly focused whilethe interbeam angles are diverging over a wide area prior to contactwith a defined volume. The system also allows for the divergence tocease prior to impact with the defined volume so that images formed inthe defined volume are not skewed due to the continued divergencebetween light beams which impact the volume at one distance from thesource and light beams which impact the volume at a different distancefrom the source.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing objects, features and technical advantages, as well asothers, of the invention will be more apparent from the followingdescription of the drawings in which:

FIG. 1 shows the optical system for a single coherent beam;

FIG. 2 shows the beams passing through positive and negative lenses;

FIG. 3 shows a multiple beam system; and

FIG. 4 shows a defined volume time displaced sequence.

DETAILED DESCRIPTION OF THE INVENTION

Before beginning a discussion of the optic system, a brief overview ofthe manner in which images are created in a defined volume isappropriate. Such a discussion is with respect to FIG. 4 where surface19, which in one embodiment can be a spinning helix, defines a volume Vas it rotates about some central point. Each point in time A, B and Cshows the same physical (spatial) place but at a slightly differenttime. Hence, the surface 19 representing the surface of the helix moveswith respect to the fixed reference frame of FIG. 4 as time progressesfrom A to B to C. Since the helix, or double helix in anotherembodiment, is spinning at a rate of 600 rpm or faster, the human eyewill treat the surface as being transparent. It is this transparency,coupled with the fact that the coherent light, upon impact with thesurface, will generate a spot of light which is visible to the humaneye, which allows for the creation of three-dimensional images.

Thus, coherent light source and optics system 10, which will bediscussed in more detail in that which is to follow, provides a pulse oflight 102 which has been spatially positioned and timed such that itimpacts with surface 19 to form a point of light 105 at a height d1 froma base line 40. This pulse could be timed to arrive a little later intime and then it would impact surface 19 to create point of light 105'which is displaced from base line 40 at a height of d2. Still furtherdelay in the beam 102 would result in a point of light 105" at a heightof d3 from base line 40.

Using this technique, then, and understanding that light source 10 candeliver multiple light beams over a wide spatial range sequentially intime, three dimensional images can be formed from the points of light.Because the spinning helix is transparent to the human eye, the lightspots will appear to be free floating and can be viewed from any angleand from any side.

The optical problem begins with the fact that the scanner has a verylimited output divergent angle and thus, it is important to amplify thatdivergence in order to fill up the display volume optically. However,when that angle is diverged, the width of the laser beam is alsodiverged which, in turn, reduces the resolution. Contrary to other wellknown lens systems for use in projecting images on the screen whichconstitute a single focal plane, the instant system produces a threedimensional image on the rotating helix which is, in one way ofthinking, a multiple or varying focal plane. Thus, the problem withprojecting the beam across the display volume is that the beam must haveas little divergence as possible so that it will be focused uponengaging the focal plane at any depth through the display volume. Suchfocus must be maintained despite the fact that it is necessary toamplify the divergence of the output from the scanner in order to fillthe X-Y axis of the volume display.

Turning now to FIG. 1, optics system 10 includes the light source whichcan be a visible light laser 11, typically an argon laser. The laserbeam enters modulator 12 that switches the laser beam on and off,synchronizing it with other elements of the system and with the spinningdisk. Lenses 13 and 14 comprise a beam expander that increases thediameter of the laser beam as an input to scanner 15. The diameter ofthe beam is the result of the trade-off between system speed andresolution. The specific beam expander magnification required isdependent on the characteristics of the scanner and the nature of theinformation to be displayed. The tradeoff between display luminance,spot size or resolution, and system speed or number of displayablevoxels, as embodied in the beam expander is a critical element of thisinvention.

Scanner 15 is an off the shelf dual access acousto-optic laser scannersuch as model LS110-XY from Isomet Corporation. Within the scanner, twoorthogonally mounted single axis deflectors sequentially deflect thebeam so that any position in X-Y angular space may be addressed. Byprojecting the resulting angles onto a screen such as the helixdescribed above, these scanned angles are mapped into X-Y displacementsin the display volume. The scale factor of the mapping is determined bythe design of the projection optics. Since the scanner addresses onlyone position at a time, the image must be built point by pointsequentially in time. Because the helical projection screen is moving,the signals directing the scanner must be scheduled so as to direct eachpoint at the proper time with respect to the screen motion to create thethree dimensional image. An electrical signal 110 from a signalprocessor (not shown) controls scanner 15. It is the subject ofconcurrently filed patent application Apparatus and Method for VolumeGraphics Display Ser. No. 07/563,372 filed Aug. 6, 1990. The diameter ofthe beam is the result of the trade off between speed and resolution.The speed of the acousto-optic scanner relates to the time required todisplay a single point of light. This depends on the acoustic velocityof the active acousto-optic medium and on the diameter of the light beamat the scanner. A larger beam diameter will require a longer displaytime than a small beam diameter given the same acoustic velocity.Similarly, the resolution of the scanner relates to the action of thescanner as a diffracting aperture. A small beam diameter will result ina larger beam divergence and a lower resolution system. As a result, asmall beam at the scanner gives a lower resolution system, but with moredisplayable points as a result of the increased scanner speed whencompared to a system with a larger beam diameter at the scanner. Theoutput of the scanner comprises several beams sequential in time thatdiverge with respect to each other. They are incident on lenses 16 and17 that comprise a projector. Lenses 16 and 17 individually narrow beams101, 102, and 103 and, at the same time, increase the divergence of thebeams from one another.

Collimator 18 then eliminates the divergence angle after the three beamshave achieved the proper separation. The beams are incident on thespinning disk in the display volume and become images 104, 105 and 106.Beams 101, 102 and 103 are able to impact any depth within the displayvolume by properly synchronizing with the spinning disk.

FIG. 2 more fully illustrates projector lenses 16 and 17. Beams 102 and103 are incident on positive lens 16. The projector (lenses 16 and 17)decreases the diameter (d-102, d-103) of the beams, when they exit theprojector as d-102' and d-103'. The projector also increases the anglefrom φ to φ' between beams 102 and 103 at the exit path. Lens 16 haslittle affect on angle φ. Lens 16 acts much like an objective lens whichto first order focuses the individual beams without changing the fieldangle. Negative power element 17 increases angle φ' and has littleeffect on the diameters of beams 102 and 103, acting much like a fieldlens which to first order does not refocus the individual beams but doeschange the field angle. While this describes the first order propertiesof the elements 16 and 17, detailed consideration of the beampropagation and geometric aberration effects are required to determinethe constructional parameters for any specific embodiment.

Returning to FIG. 1, as diverging beams 101, 102, and 103 leave negativelens 17, they continue to diverge. Therefore, if the display volume wereto be placed in the beam path directly after lens 17, the image formedon different sides of the display volume would have different lengthsand thus be distorted. This problem has been solved by using collimator18 that stops the divergence after length 1 and makes the beams 101,102, 103 parallel to each other. Length 1 can be adjusted, not shown, tochange the divergence angle.

While collimator 18 has been shown as a curved mirror surface, it couldbe any one of several different arrangements. For example, collimator 18could be a large refractive element, a Fresnel optic, or a holographicoptic.

Turning now to FIG. 3, a three color or multicolor system is shown. Thesecond and third color beams 301 and 302, respectively, each have theirown laser beam modulator 32, 40, beam expander 33, 34 and 41, 42,scanner 35, 43 and are folded by a mirror 37, 45 from their own pathinto the path of the first color between lenses 16 and 17. The beamsplitters 38, 46 that are located between lenses 16 and 17 are standarddichroic type beam splitters. The output of the light path from lens 17can be any single beam 102, 301 or 302 or any combination 102, 301 and302; 102 and 301; 102 and 302; or 301 and 302 thereof.

Although the present invention has been described with respect to aspecific preferred embodiment thereof, various changes and modificationsmay be suggested by one skilled in the art, and it is intended that thepresent invention encompass such changes and modifications as fallwithin the scope of the appended claims.

What is claimed is:
 1. An optics system for use in creating images from coherent light in a defined volume display, said system comprising:a coherent light source; a scanner for spatially displacing individual beams of said coherent light; a first lens for compacting the beam width of each such spatially displaced light beam; a second lens for amplifying the spatial displacement of each such spatially displaced light beam without changing said compacted beam width; and a spinning disk defining a display volume, said spinning disk intersecting said light beam at different depths in the display volume for producing a three dimensional image.
 2. The system as set forth in claim 1 wherein said system further comprises:a collimator for accepting said spatially displaced light beams and for converting said light bursts into parallel light beams.
 3. The system set forth in claim 1 wherein said system further comprises:a collimator for modifying said displacement angle of said diverging light beams.
 4. A system for presenting coherent light beams to a defined volume, such that the presented beams will impact the volume at different distances from the light source to form a three dimensional image within the defined volume, said system comprising:a scanner for spatially displacing individual beams of coherent light, each beam having a particular time and spatial orientation, said spatial orientation measured as a divergence angle from a center line; a first positive lens for creating a narrow waist with respect to each light beam emerging from said scanner; a second negative lens for increasing each divergence angle while still maintaining each said narrow waist; and a spinning disk defining a display volume, said spinning disk intersecting said light beams at different depths in the display volume for producing a three dimensional image.
 5. The system set forth in claim 4 further comprising:a light beam divergence angle modifier for changing the angle of said divergence angle.
 6. The system set forth in claim 4 wherein said system further includes:a processor for generating a plurality of signals each for controlling the depth of a light beam with said disk as well as the spatial positioning of said light beams and wherein said signals control said scanner.
 7. The method of operating an optic system for creating images from coherent light in a display volume defined by a spinning disk, said method comprising the steps of:accepting coherent light beams; spatially displacing individual light beams of said coherent light; compacting the beam width of each such spatially displaced light beam; amplifying the displacement angle of each such spatially displaced light beam without changing said compacted beam width; and projecting each said light beam, which has had the beam width compacted, into said display volume, intersected by the spinning disk, and forming a three dimensional image.
 8. The method set forth in claim 7 wherein said method further comprises:accepting said spatially displaced light beams and converting said light beams into parallel light bursts for introduction in said defined display volume.
 9. A method for creating coherent light spots within a well-defined display volume to form a three dimensional image within the defined display volume, said method comprising the steps of:spatially displacing individual beams of coherent light, each having a particular time and spatial orientation, said spatial orientation measured as a divergence angle from a center line; creating a narrow waist with respect to each said displaced light beam; increasing each divergence angle while still maintaining each said narrow waist; and projecting said displaced light beams, with narrow waists, into said display volume, said light beams traveling varying distances before impacting a moving surface within said display volume.
 10. The method set forth in claim 9 further comprising the step of:changing said divergence angle of each said light beam.
 11. The method set forth in claim 10 wherein said divergence angle is changed a different amount for each said displaced light beam.
 12. The method set forth in claim 10 further comprising the step of:controlling the magnitude of the total divergence of all said displaced light beams. 